1. Field of the Invention
The present invention relates to a stereoscopic endoscope which is used for stereoscopic observation of objects.
2. Description of the Related Art
In recent years, endoscopes for medical use, which enable the interior of a body cavity to be observed by inserting a long thin inserting section into the body cavity, have been widely used. Such an endoscope makes it possible not only to observe the interior of the body cavity but also to perform various types of medical care and treatment by using a treating instrument that is inserted into an instrument channel provided in the endoscope. Apart from this, endoscopes for industrial use are being used to observe or inspect flaws, corrosions, etc. inside the piping in boilers, chemical plants or the like, or inside the engines of automobiles, airplanes, etc.
Such endoscopes are divided into two types based on the relative hardness of the inserting section: elastic type endoscopes whose inserting section is elastic so that it can be inserted into the body cavity, which is full of twists and turns, from the oral cavity, etc.; and rigid type endoscopes whose inserting section is made rigid so as to be linearly inserted toward the section of the object to be observed.
A flexible image guide fiber is used as the optical image transmission means of the elastic type endoscope. In the rigid type endoscope, which has a rigid inserting section, a relay optical system is used as the image transmission means.
Further, endoscopes may be divided into two types based on the means of observation used: optical endoscopes with which the image is directly observed by the naked eye; and electronic endoscopes which use a solid-state image sensing device, such as a CCD (charge-coupled device), as the imaging means.
The above-mentioned conventional endoscopes have a problem in that the image thereby obtained during the observation of the interior of the body cavity is mostly a planar image having no depth. Thus, in endoscopic observation, it is rather difficult to observe the minute surface irregularities of the inner wall of the body cavity, which surface irregularities are an important diagnostic index.
To cope with this problem, stereoscopic endoscopes which make it possible to observe the minute surface irregularities of the inner wall of the body cavity have been proposed.
Japanese Patent Laid-Open No. 57-69839 discloses a stereoscopic endoscope in which eyepieces are provided at the ocular end of a pair of image guides arranged inside the inserting section, and objective lenses are provided at the other end thereof on the front-end side of the inserting section, so as to enable the interior of the body cavity to be stereoscopically observed. With this stereoscopic endoscope, it is possible to stereoscopically observe the inner wall surface of an object by adjusting the angle of convergence made by the point of observation and the pair of objective lenses in such a way as to enable stereoscopic observation. This stereoscopic endoscope is applied to an elastic type endoscope.
In a rigid type endoscope which enables an object to be stereoscopically observed, a pair of relay optical systems are arranged in parallel inside the inserting section of the endoscope, the images respectively obtained by these relay optical systems being picked up by image sensing devices such as CCDs. In this stereoscopic endoscope, electric signals representing the images formed on the image sensing devices are converted into image signals, which are displayed on a monitor, thereby making it possible to perform stereoscopic observation.
U.S. Pat. No. 4,924,835 discloses a stereoscopic endoscope which includes a pair of light transmission devices and shutters corresponding to the pair of light transmission devices, wherein the images respectively obtained by the transmission devices are alternately shaded by the shutters, thereby enabling an object to be stereoscopically observed.
Thus, in these stereoscopic endoscopes, stereoscopic observation is made possible by obtaining left and right images of the object through use of a pair of optical systems, a pair of CCDs, etc.
In the stereoscopic endoscope of the type which is provided with a pair of CCDs, the vertical dimension (the top-to-bottom relationship) of the image is determined by the position of the CCDs. As a result, the top-to-bottom relationship of the image as displayed on the monitor does not always agree with that of the monitor. Therefore, when the endoscope for observing the interior of the body cavity is rotated around the optical axis of the endoscope, the orientation of the CCDs inside the inserting section varies to change the visual-field direction, so that the image displayed on the monitor turns upon the rotation of the endoscope, resulting in there being a disparity between the top-to-bottom relationship of the monitor and that of the image.
Thus, the operator cannot immediately understand the positional relationship between the endoscope and the interior of the body cavity by glancing at the image displayed on the monitor, so that it is rather difficult to set, for example, the treating instrument, inserted through the instrument channel of the endoscope, quickly and correctly at a desired position.